FDisk Dos Commands

Undocumented switches you can use with FDISK. With the switches you can use FDISK in non-interactive mode, e.g. in a batch file.

The switches works with the FDISK that is include with Windows 95 OSR2 (MS-DOS 7.1)

Variables used in this document:

<size> Partition size in Mb - FDISK rounds this number up

<disk> Harddisk number, e.g. first HD is number 1

/STATUS

Show current partition layout

/MBR

Recreate Master Boot Record on disk 1

/PRI

Create primary partition

/PRIO

Create primary partition with FAT16/FAT32 override

/EXT

Create extended partition

/LOG

Create logical drive

/LOGO

Create logical drive with FAT16/FAT32 override

/FPRMT

Prompt for FAT32/FAT16 in interactive mode

/Q

Skip forced reboot on exit

/X

Do not use LBA partitions

/ACTOK

Do not check drive integrity

/CMBR

Recreate Master Boot Record on specified disk

Notes on /PRI, /PRIO and /LOG, /LOGO

As far as I can tell, PRI and LOG creates FAT32 when partitions are larger than 512Mb and FAT16 when partitions are smaller than 512Mb. PRIO and LOGO creates FAT16 even if partitions are larger than 512Mb (in effect, it’s like FDISK from DOS 5/6).

/STATUS - Show current partition layout

If you have an extended partition with no logical drive defined, no information about the extended partition is shown

FDISK /STATUS

/MBR - Recreate Master Boot Record on disk 1

This function is handy when an virus has infected the Master Boot Record. With /MBR you can wipe-out the virus.

FDISK /MBR

PRI - Create primary partition. Partition is set to active

Create a primary partition on disk number <disk> with the size of <size>. The partition is set to active.

If <size> is larger than the space on the HD all space is used for the primary partition.

FDISK /PRI:<size> <disk>

/PRIO - Create primary partition with FAT16/FAT32 override. Partition is set to active

Works as /PRI.

/EXT - Create extended partition

Create an extended partition (to hold logical drives) on disk number <disk> with the size of <size>.

If <size> is larger than remaining free space, all free space is used. That is, you don’t have to know the exact remaining size in order to use this switch.

FDISK /EXT:<size> <disk>

/LOG - Create logical drive

With /LOG you create a logical drive with the size of <size>. /LOG must be used together with /EXT.

/LOG must be used together with /EXT and <size> must be the same for both switches. Furthermore, <size> must be smaller or equal to free space.

FDISK /EXT:<size> <disk> /LOG:<size>

/LOGO - Create logical drive with FAT16/FAT32 override

Works as /LOG.

/FPRMT - Prompt for FAT32/FAT16 in interactive mode

With /FPRMT you won't get the FDISK startscreen where you are asked for support for large disks. Instead, you will be promted for FAT16/FAT32 each time you create a partition.

FDISK /FPRMT

Note that the prompt for FAT16/FAT32 will be available for ALL partitions, so this option can be used to force FDISK to create FAT 32 partitions smaller than 540Mb. (By default, FDISK uses FAT32 for partitions greater than 540Mb only).

/Q - Skip forced reboot on exit

With /Q the PC will not be rebooted after modifying the Partition Tables. However, I don't recall that DOS 7.x FDISK does a reboot. Maybe it's because I always use FDISK from a boot-floppy.

FDISK /Q

/X - Do not use LBA partitions

With /X you won't get any LBA partitions. See Micro Firmware Technical Support for more details.

FDISK /X

/ACTOK - Do not check drive integrity

With /ACTOK the integrity of drive is not checked making FDISK faster.

It may not work everytime.

FDISK /ACTOK

/CMBR - Recreate Master Boot Record on specified disk

Works as /MBR with the exception that you specify the disk to have it's MBR recreated.

FDISK /CMBR <disk>

Piping Keystrokes

You can pipe keystrokes into FDISK using a file which contains the keystrokes including <CR>.

Most editors can't insert the <CR> character without <LF> so you need a hex-editor to do the job.